Large-Scale Experimental Simulations of In Situ Coal Gasification in Terms of Process Efficiency and Physicochemical Properties of Process By-Products

This paper presents a series of surface experiments simulating underground coal gasification (UCG). The main goal of the experiments was to investigate the influence of the gasification medium and the coal rank on the gasification process. Four multi-day trials were carried out using a laboratory gasification facility designed for the large-scale experimental simulations of UCG and located in the Experimental Mine "Barbara", located at Mikolow, Poland. Two Polish bituminous coals were investigated: coal sourced from "Piast-Ziemowit" mine and coal sourced from "Wesola" mine. Each of the two coals was gasified in two separate experiments using oxygen-enriched air (OEA) and pure oxygen as the respective gasifying agents. Gasification with oxygen resulted in significantly higher gas quality and higher process efficiency than gasification with OEA. Higher concentrations of hydrogen (23.2% and 25.5%) and carbon monoxide (31.8% and 33.4%) were obtained when oxygen was used as a gasifying reagent, while lower concentrations were obtained in the case of gasification with OEA (7.1% and 9.5% of hydrogen; 6.4% and 19.7% of carbon monoxide). Average gas calorific values were 7.96 MJ/Nm(3) and 9.14 MJ/Nm(3) for the oxygen experiments, compared to 2.25 MJ/Nm(3) and 3.44 MJ/Nm(3) for the OEA experiments ("Piast-Ziemowit" coal and "Wesola" coal, respectively). The higher coalification degree of "Wesola" coal (82.01% of carbon) compared to the "Piast-Ziemowit" coal (68.62% of carbon) definitely improves the gas quality and energy efficiency of the process. The rate of water condensate production was higher for the oxygen gasification process (5.01 kg/h and 3.63 kg/h) compared to the OEA gasification process (4.18 kg/h and 2.63 kg/h, respectively), regardless of the type of gasified coal. Additionally, the textural characteristics (porosity development) of the chars remaining after coal gasification experiments were analyzed. A noticeable development of pores larger than 0.7 nm was only observed for the less coalified "Piast-Ziemowit" coal when analyzed under the more reactive atmosphere of oxygen.